Processes and apparatuses for preparing sulfuric acid are known in various embodiments from industrial practice. In this preparation or industrial preparation of sulfuric acid, a catalytic oxidation of sulfur dioxide to sulfur trioxide takes place. Here, vanadium pentoxide (V2O5) is generally used as catalyst. Such catalysts are active only above particular relatively high temperatures. Thus, vanadium pentoxide is active only above a temperature of about 410° C. On particular occasions, for example for maintenance of the apparatus, the production of sulfuric acid has to be interrupted. Nevertheless, the apparatus should be kept hot during such a production downtime in order to avoid, in particular, condensation of sulfuric acid and corrosion resulting therefrom. Furthermore, the catalyst firstly has to be heated to the required activation temperature on starting up such an apparatus.
Keeping such an apparatus hot or heating it during a production downtime and also on starting up the apparatus using heated and dried atmospheric air is known from the prior art. Here, humid atmospheric air from the surroundings is dried with the aid of concentrated sulfuric acid. For this purpose, relatively large amounts of concentrated sulfuric acid have to be kept in stock in a disadvantageous manner and correspondingly large sulfuric acid tanks are required for this purpose. In order to avoid corrosion, the sulfuric acid used for drying the air has to have a concentration of not less than about 93%. Adhering to this limit is frequently problematical. If moisture or humid atmospheric air intrudes into the apparatus, the corresponding water forms sulfuric acid or dilute sulfuric acid by reaction with the sulfur trioxide present in the apparatus components and the result can be considerable corrosion which, at least in the long term, can bring the usability of apparatus components into question.
Thus a need exists for a process by means of which the flow paths and the components of the apparatus concerned can be heated or kept hot in a simple manner with little outlay and in which the disadvantages indicated above can be avoided. A need also exists for a corresponding apparatus for carrying out this process.